1. Field of the Invention
The present invention generally relates to image sensors, and more particularly to a system and method for generating a color correction matrix for an image sensor.
2. Description of the Prior Art
In order to achieve high fidelity of colors, an image sensor must behave very similarly to the human eye such as to meet standard color responses defined by the CIE (Commission internationale de l'éclairage or International commission on Illumination) as color matching functions (CMFs). The CMF quantifies the color of each single wavelength in the human visible band (e.g., 380-750 nm) in terms of a set of, for example, R, G, B (red, green, blue) primaries. Each set of primaries defines a color space, which may partially (e.g., sRGB or NTSC) or completely (e.g., XYZ) cover the colors perceptible by the human eye.
A color may be represented by a point in a color space, and may be mapped to different color spaces. In reality, the sensor CMF usually deviates from the human eye response. A fitting algorithm, accordingly, has to be adopted to obtain a color correction matrix (CCM) in order to achieve minimum color perception error.
Another process essential to obtaining proper color perception is the white balance (WB), which equalizes the R, G, B color channels to restore the ideal white response of a non-ideal image sensor.
Conventional approaches to the CCM and the WB are commonly based on system-level measurement, in which a standard color chart, such as the 24-patch Macbeth ColorChecker, is used as a target. The image sensor achieves WB by a white or gray patch, and the sensor's R, G, B outputs of other color patches are compared with the human response. A fitting technique is then used to produce the CCM.
One of the disadvantages of the conventional system-level measurement system is the associated complex calibration and maintenance schemes and efforts required to prevent physical measurement errors.
For the reason that conventional measurement systems and methods cannot effectively provide the CCM and the WB with satisfactory accuracy, a need has arisen to propose a novel scheme for simplifying and improving the CCM and WB processes with high accuracy.